1. Field of the Invention
The invention relates to the making of fast crystallizing polyalkyleneterephthalate resin compositions useful in molding applications. More particularly, this invention relates to the preparation of fast crystallizing polyalkyleneterephthalate molding compounds containing a complex of a sodium carboxylate and an organic compound such as a polymeric compound containing an ethyleneoxy repeating unit --CH.sub.2 CH.sub.2 O--, together with appropriate reinforcing agents, fillers and/or additives.
2. State of the Prior Art
Polyalkyleneterephthalates have acquired considerable attention as starting materials for the preparation of film, and shaped articles due to their outstanding mechanical and thermal properties. However, polyethyleneterephthalate is known to have a very slow crystallization rate at temperature below 130.degree. C. so that when low molding temperatures and short residence times are employed, the molded article has low crystallinity and poor surface smoothness. The resultant necessity to use high mold temperatures and long residence times has, for a long time, discouraged the use of polyethyleneterephthalates as a molding resin despite its high mechanical and thermal properties.
Polypropyleneterephthalate and polybutyleneterephthalate both have fast crystallization rates, but their crystallization rates and degree of crystallinity still need to be improved, especially for molding very thin parts at low temperatures.
The effectiveness of a crystallization promoter can be studied by measuring the melt and cold crystallization rates of the polyalkyleneterephthalate resin compositions. A much more convenient way is to measure the melt and cold crystallization temperatures of the compositions. Conventionally, the melt crystallization temperature can be determined by following the heat capacity change of the melt in a calorimeter. The maximum of the exotherm during the slow cooling of the melt is taken as the melt crystallization temperature (T.sub.mc). The maximum of the exotherm during a more rapid heating of an amorphous polyalkyleneterephthalate is taken as the cold crystallizing temperature (T.sub.cc). To obtain the amorphous or glassy polyalkyleneterephthalate, the resin has first to be completely melted and then quickly quenched, for instance, by dropping the melt into dry ice. It should be noted that both the obtained melt and cold crystallization temperatures depend not only on the history (melt temperatures, annealing, etc.) of the specimen, but also on the heating and cooling rate of the measurement. Thus, for studying the effectiveness of a crystallization promoter, these conditions have to be fixed for purposes of direct comparison. These temperatures are obtainable using a differential scanning calorimeter.
Due to the low heat conductivity of the polymer molding compounds, the inside portion of the resin during molding usually experiences a slower cooling rate than the surface of the molded article. The study of the melt crystallization thus can provide information relating to inside portions, whereas the study of the cold crystallization can provide information relating to the surface of the molded article. A desirable crystallization promoter will substantially increase the melt crystallization temperature and decrease the cold crystallization temperature of polyalkyleneterephthalate resin compositions.
Herwig's U.S. Pat. No. 3,761,450 describes the use of the sodium salt of a polycarboxylic acid as a nucleation agent for polyalkyleneterephthalate. Ibbotson demonstrates that sodium stearate can reduce the cold crystallization temperature of polyethyleneterephthalate (Journal, British Polymer, ii, 146 (1979). United Kingdom Patent Application No. 2,075,032 proposes that the alkali metal salts of a fatty acid can be used as nucleation agents for polyethyleneterephthalate. U.S. Pat. No. 4,352,904 describes sodium or potassium salt of a hydrocarbon acid as a nucleation agent for polyethyleneterephthalate molding compounds. Tonoki's U.S. Pat. No. 4,362,839 teaches the use of alkali metal carboxylates as nucleating agents. Lu's U.S. Pat. No. 4,351,758 teaches the use of alkali metal salts such as the carbonates, bicarbonates, silicate oxides, oxides, etc. as nucleating agents.
Applicant's U.S. Pat. No. 4,365,036 shows as a nucleating agent, a complex formed between NaI and a polyethylene oxide and patent application Ser. No. 420,569, filed Sept. 20, 1983, now U.S. Pat. No. 4,405,741, teaches the use of a complex formed between sodium thiocyanate (NaSCN) and a polyethylene oxide. However, although the use of sodium salts of carboxylic acids are shown in the above-cited prior art references, there is no teaching that polyethylene oxide complexes of sodium carboxylates will be effective as nucleating agents. In fact, it is not known which of the prior art nucleating agents are capable of forming polyethylene oxide complexes and whether such complexes will be superior as nucleating agents as compared to the non-complexed nucleating agent.